You won't find that name on any map, though, for it was changed many years ago. Long before the coming of the white man to the area the natives grazed their horses on the plains of the valley in the winter because of its mild and relatively snow free winters. When the fur traders arrived they did the same and the valley, then the town, acquired the name Wild Horse Plains. After some time that was shortened to Horse Plains then, about 1905, to simply Plains.

The first fur traders arrived in the area in 1810, eventually moving on to be replaced by the first settlers in 1867. The town did not begin to grow until 1883, with the arrival of the Northern Pacific Railroad. The next town south, Paradise, was granted the title of Division Point by the railroad, so grew faster and larger than Plains. When the division point was removed from Paradise and the locomotive shops and railroad yards closed, Paradise began the shrink, while Plains continued to grow. While, in the late '30s the town was the "largest and oldest white community west of Missoula in the Clark Fork Valley", it has since been overtaken by Thompson Falls, the seat of Sanders County and site of the Thompson Falls Hydro Dam.

Today Plains remains a quiet little town of just over 1,000 residents. The only buildings of any real age remaining in the town are a stone jail, built in the 1900s, the original log schoolhouse, dating from 1878 and the Methodist Church, its hall having been built in 1896 and the sanctuary in 1904. Also in the town today are a VFW, a shared Grange & Masonic Hall, a newspaper, the Clark Fork Valley Press, sports facilities, a Seniors' Centre, a couple of parks, a swimming pool, several churches, eateries, pizza and burger joints and the Clark Fork Valley Hospital. The town's only grain elevator (unless there were once more) still stands and is now the visitor centre and antique shop.

The entry from the American Guide Series book Montana, A State Guide Book follows.

PLAINS, 39.8 m. (2,582 alt, 522 pop.), straddles the highway, its business houses R., the railroad L. Beyond the stores are trim, neatly painted, frame dwellings, churches, and a school. Plains is the largest and oldest white community west of Missoula in the Clark Fork Valley, which at this point is about 15 miles wide. Because of the large herds of wild horses that once ranged the valley, the flats and town were originally called Wild Horse Plains. The Kootenai Trail ran near the site.
From Montana, A State Guide Book, Page 335